Re: Audio mixer and mixer control

[O'Connor, Daniel via freebsd-stable]

> On 11 Apr 2020, at 17:28, Harry Schmalzbauer <free...@omnilan.de> wrote:
> Hello and thanks for your help.  Main issue is to playback simultaniously on 
> more than one dsp (musicpd(1) is providing that feature out of the box, but I 
> was looking for a more general way, covering mixed line-in (DAB+ radio)).

I am not sure there is a general solution in the kernel.

> Here's my sndstat:
> FreeBSD Audio Driver (64bit 2009061500/amd64)
> Installed devices:
> pcm0: <Realtek ALC892 (Rear Analog 5.1/2.0)> on hdaa0  (1p:2v/1r:2v) default
> pcm1: <Realtek ALC892 (Front Analog)> on hdaa0  (1p:2v/1r:1v)
> pcm2: <Realtek ALC892 (Internal Digital)> on hdaa0  (1p:1v/0r:0v)
> pcm3: <Realtek ALC892 (Rear Digital)> on hdaa0  (1p:1v/0r:0v)
> pcm4: <USB audio> at ? kld snd_uaudio (0p:0v/1r:1v)
> No devices installed from userspace.

OK, looks fairly normal..
BTW you can get more information with..
sudo sysctl hw.snd.verbose=2
cat /dev/sndstat

> To my surprise, today there's dsp0_line-in/mix signal on dsp1_line-out. No 
> idea if it was a layer 8 error yesterday (pretty sure it was not) or if some 
> smart chip on the mainboard decided to interconnect over night (no reboot)?!? 
> In fact, adjusting "mix" on dsp0 controls the output volume on dsp1 (analog 
> line-in on dsp0 get's somehow routed to analog out on dsp1 (killed 
> pulseaudio, nothing else is running, so it must be done in hardware)).

That sounds pretty peculiar, I guess it could be an result of the fact your 4 
PCM devices are really 1 piece of hardware..

> I'd like to share what I discovered while browsing freshports.org/audio:
> rawrec(1) might be the leanest way to pipe signals, like you mentioned using 
> sox(1).

Yep, looks like it.

> virtual_oss(8) seems to do exactly what I was looking for regarding "mixing". 
> No idea how cuse(3) comes into play, seems to be not as native as I prefer 
> things.

Yes, it does - I haven't used it but it looks like what you want.

cuse is for allowing device drivers in user land, I don't think it's required 
for virtual_oss, just that the same author wrote both :)

> Unfortunately, I don't have time to play with at the moment.  But once I come 
> back to it, I'll find it here for reference ;-)

Good find, best of luck!

--
Daniel O'Connor
"The nice thing about standards is that there
are so many of them to choose from."
 -- Andrew Tanenbaum


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